1. Field of the Invention
The invention relates to temperature sensor devices for motors. More particularly, the invention relates to a temperature sensor for a motor having a simplified structure.
2. Description of the Related Art
Motors are used to power actuators that drive such things as power windows and power lift gates in motor vehicles. With the advent of low cost microprocessor controls, motors often contain Hall Effect encoders to deliver speed and positional information to an electronic controller. A Hall Effect signal is a digital square wave corresponding exactly to the motor's rotational movement, having alternating high (VH) and low (VL) logic levels. From this Hall Effect signal, identifying the exact speed and rotational position of the motor can be determined.
Motors used in similar actuators also often require thermal protection to protect the motors from abuse and overload conditions. Motors may include discreet internal devices to interrupt current in case internal temperatures reach dangerous levels for the integrity of the motor. Both solid state and bi-metal devices are available. Such devices carry motor currents directly and are generally large, costly, and can be imprecise to a temperature limit. Such devices, in series with motor currents, introduce undesirable voltage drops, critical in low voltage applications such as automotive powered battery systems.
Referring to FIGS. 1A and 1B, a Hall Effect sensor uses an internal transistor to amplify the Hall Effect and generate a digital signal. The transistor is an open collector transistor and switches between open and close conditions to ground generating a wave form signal to the controller through a series resistor or a pull-up resistor. When the transistor is off, the signal level is high; and, when the transistor is conducting, a current flow causes voltage to be dropped across the pull-up resistor creating the low signal level. FIG. 1B illustrates the output of this device.
Referring to FIGS. 2A and 2B, certain Hall Effect applications use an internal resistor in conjunction with the pull-up resistor so that only two wires are necessary to connect to the Hall Effect sensor. The signal generated by the Hall Effect sensor is transmitted on the power feed wiring by using an intermediate voltage for the low logic level. With this, the Hall Effect sensor is continuously powered by the low and high logic levels.